Noise control apparatus

Abstract

A noise control apparatus for reducing a sound volume of a noise propagating from a noise source such as a railroad includes a sound arresting wall placed apart from the noise source. Means for shifting in phase and refracting the acoustic wave of the noise is disposed at substantially the top of the noise arresting wall. The above means, for example, has a plurality of passageways extending substantially along the propagating direction of the acoustic wave of the noise and the length of the passageways varies. Through the above means, a part of the acoustic wave from the noise source is refracted and the phase thereof is shifted to be a refracted propagating sound, which thereafter interferes with the other part of the acoustic wave directly from the noise source to thereby reduce a sound volume to a great extent.

What is claimed is: 
     
       1. A noise control apparatus for reducing sound volume of noise propagating from a noise source, comprising: a sound arresting wall separate from the noise source; and   means for shifting in phase and refracting the acoustic wave of the noise to provide a refracted propagating acoustic wave, said means being disposed at substantially the top of said sound arresting wall, said means being hollow and further comprising bent plates vertically disposed within said means, said bent plates having an equal interval therebetween and having front edges aligned in such a manner that a line drawn through the front edges diagonally descends and intersects with said noise source,   whereby said refracted propagating acoustic wave interferes with said acoustic wave directly propagating from the noise source and diffracting over said sound arresting wall.   
     
     
       2. A noise control apparatus as set forth in claim 1, wherein said sound arresting wall comprises a sound absorbing member on the inner side thereof facing the noise source. 
     
     
       3. A noise control apparatus as set forth in claim 1, further comprising a sound insulating member placed behind said means to isolate said refracted propagating sound downwardly propagating from said means. 
     
     
       4. A noise control apparatus as set forth in claim 1 or 3 wherein said means is disposed on the top of said sound arresting wall. 
     
     
       5. A noise control apparatus as set forth in claim 1 or 3 wherein said means is disposed at inner upper side of said sound arresting wall, and said sound insulating member is the upper portion of said sound arresting wall. 
     
     
       6. A noise control apparatus as set forth in claim 1, wherein said means is integrally formed on said sound arresting wall. 
     
     
       7. A noise control apparatus as set forth in claim 1, wherein said sound arresting wall placed about 2.7 m apart from the noise source and extending about 2.8 m from the noise source.